British warship docks in Gibraltar amid Spain row

British frigate HMS Westminster docked in Gibraltar on Monday in a naval exercise coinciding with a furious diplomatic row with Spain over sovereignty and fishing rights in the surrounding waters.

The frigate, equipped with a Type 23 weapons system including a magazine torpedo launcher, Harpoon anti-ship missiles, Sea Wolf surface-to-air missiles and helicopter, arrived at the British outpost in the morning.

Though long-planned, the visit by the warship came at a time of high tension, a day after dozens of Spanish fishing boats sailed to waters around the "Rock" to demand Gibraltar remove 70 concrete blocks it has dropped in their fishing grounds.

A cordon of British naval and Gibraltar police patrols blocked about 40 Spanish fishing boats from entering deep into disputed waters in Sunday's protest. No incident was reported beyond an exchange of insults between the two sides.

The Gibraltar government says the concrete reef will regenerate marine life and argues that the Spanish raked for shellfish there illegally. The Spaniards say they have been cut off from rich fishing grounds, hurting their livelihoods.

Spain has since imposed intense customs checks at the border to Gibraltar, leading to daily hours-long queues of cars.

British Prime Minister David Cameron described the border checks as "politically motivated" and has pressed the European Union to send observers to the border as soon as possible.

It is the latest in a string of diplomatic rows over the self-governing British overseas territory, which measures just 6.8 square kilometres (2.6 square miles) and is home to about 30,000 people.

Both Britain and Spain say the naval visits are unrelated to their differences over Gibraltar.

With Madrid's prior agreement, British helicopter and commando carrier HMS Illustrious on Sunday stopped at a Spanish naval base in Rota in southern Spain for a technical stop of several hours before leading naval exercises in the Mediterranean.

The HMS Westminster, which was accompanied by two smaller support vessels also docking in Gibraltar, is also taking part in the naval exercise, codenamed Cougar '13, which was planned long before the latest row broke out.

The British ships will visit several ports, carrying out an exercise with the Albanian armed forces before heading through the Red Sea, Indian Ocean and the Gulf for exercises with other British allies.

Spain ceded Gibraltar to Britain in perpetuity in 1713 but has long argued that it should be returned to Spanish sovereignty. London says it will not do so against the wishes of Gibraltarians, who are staunchly pro-British.